1. Field of the Invention
The present invention relates to a communication system, and more particularly to an IPv6 (Internet Protocol, version 6) based communication system and method for setting an address and selecting a source address effectively when an IPv6 based host (node) moves between host networks.
2. Description of the Related Art
In a Request for Comments (RFC) 2460 (Obsoletes: 1883) standard, an IPv6 (Internet Protocol, version 6) supports mobility by itself. In the IPv6 specification, a global address can be directly created through ND (Neighbor Discovery), AAC (Address Auto-Configuration) and DAD (Duplicate Address Detection) mechanisms. In other words, IPv6 accommodates the concept of a mobile Internet protocol associated with a home network, HA (Home Agent), CoA (Care of Address), etc. All hosts should support the AAC and ND mechanisms. These mechanisms are outlined below.
ND Mechanism
The ND mechanism is directed to an ARP (Address Resolution Protocol) in IPv4 (Internet Protocol, version 4) and is a protocol for identifying network topology variations and measuring link states. The ND mechanism retains reachable information on paths linked to neighbor nodes being activated and identifies circumferential routers and prefix information. There are five ND related messages including an RA (Router Advertisement) message to be used for identifying whether there is another router attached to the same link as a router's link, an RS (Router Solicitation) message, an NS (Neighbor Solicitation) message for performing the same function as the ARP in IPv4, an NA (Neighbor Advertisement) message, and a redirect message to be used in the case that the router recognizes a better path. The router transfers its own prefix information to its circumferential hosts through the RA message.
AAC Mechanism
The AAC mechanism automatically creates a routable address and automatically sets a default router with a “Plug-and-Play” function of IPv6 that does not require assigning an address to a host. The AAC mechanism is an optional mechanism using the ND mechanism described above. The AAC mechanism can provide many advantages in that it configures and manages a network by identifying a prefix, default router and address duplication.
An IPv6 address is configured as shown in FIG. 1. Referring to FIG. 1, the IPv6 address is made up of a network prefix of n out of 128 bits and an interface identified (ID) having (128−n) bits.
FIG. 2 is a view explaining an address auto-configuration procedure. A procedure of creating a global IPv6 address is now described below with reference to FIG. 2. First, the lower-order 64 bits in the global IPv6 address are configured using a 48-bit MAC (Media Access Control) address of 128 bits. In IPv6 on the Internet, the interface ID represents an EUI-64 based interface It). More specifically, a lower-order 64-bit interface ID “02:90:27:ff:fe:17:fc:0f” of the global IPv6 address is acquired by adding the 2-bytes “ff:fe” in the middle of a 48-bit MAC address “00:90:27:17:fc:0f” and setting a seventh bit b1 from a highest-order bit located within a highest-order byte “00” to “1”. The seventh bit b1 from the highest-order bit located within the highest-order byte “00” represents a U/L (Universal/Local) bit for indicating a unique address. The lower-order 64-bit interface ID “02:90:27:ff:fe:17:fc:0f” described above is the same as that shown in FIG. 3 and an Interface ID for an IPv6 address shown in FIG. 1.
Referring now to FIG. 4, an example of the AAC mechanism is described as follows. In FIG. 4, an Internet ID of a host 40 is “250:daff:fe93:af5e” and a network prefix, which is received from the router 42 and carried by the RA message of the ND, is “3ffe:2e01:2:1::/48”. In other words, the host 40 configures its own IPv6 address through the AAC mechanism and the configured IPv6 address is “3ffe:2e01:2:1:250:daff:fe93:af5e”.
As shown in FIG. 5, when an IPv6 based host 50 moves from a network A 54 including a router A 52 to a network B 56 including a router B 58, it identifies an operating state of a link using the ND mechanism and receives the RA message from the router B 58 included in the network B 56. Here, the network can be a small-scale sub-network or a large-scale sub-network capable of being managed by one router. In other words, the network means a range in which one router can advertise the network prefix. Further, the host 50 configures its own IPv6 address through network prefix information and the AAC mechanism. At this time, the host 50 can transmit the RS message to the router B 58 before it receives the RA message.
As described above, an IPv6 based host waits for an RA message for a predetermined time interval immediately after moving from one network to another network in order to configure a global IPv6 address. If the IPv6 based host fails to receive the RA message after the time interval, it transmits an RS message and receives the RA message. Thereafter, the IPv6 based host configures its own address using the AAC mechanism.
However, the IPv6 based host conventionally needs various mechanisms and a lot of time to configure the address. When considering a mobile IPv6, a host incurs overhead due address configuration. Further, there is a problem when the IPv6 based host conventionally selects a source address. That is, when several IPv6 addresses are set for interfaces as a feature of IPv6, there is a significant problem arising from the difficult an IPv6 based host has in identifying which address should be selected as a source address.